DRAFT
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DTMF: In-band & Out-of-Band (RFC 2833) (SIP INFO *)
The SPA may relay DTMF digits as out-of-band events to preserve the fidelity of the digits. This can
enhance the reliability of DTMF transmission required by many IVR applications such as dial-up banking
and airline information.
Call Progress Tone Generation
The SPA has configurable call progress tones. Parameters for each type of tone may include number of
frequency components, frequency and amplitude of each component, and cadence information.
Call Progress Tone Pass Through
This feature allows the user to hear the call progress tones (such as ringing) that are generated from the
far-end network.
Jitter Buffer – Dynamic (Adaptive)
The SPA can buffer incoming voice packets to minimize out-of-order packet arrival. This process is known
as jitter buffering. The Jitter Buffer size will proactively adjust or adapt in size depending on changing
network conditions.
The SPA has a Network Jitter Level control setting for each line of service. The jitter level decides how
aggressively the SPA will try to shrink the jitter buffer over time to achieve a lower overall delay. If the
jitter level is higher, it shrinks more gradually. If jitter level is lower, it shrinks more quickly.
.
Voice Activity Detection with Silence Suppression & Comfort Noise
Generation
Voice Activity Detection (VAD) and Silence Suppression is a means of increasing the number of calls
supported by the network by reducing the required bi-directional bandwidth for a single call. VAD uses a
very sophisticated algorithm to distinguish between speech and non-speech signals. Based upon the
current and past statistics, the VAD algorithm decides whether or not speech is present. If the VAD
algorithm decides speech is not present, the silence suppression and comfort noise generation is
activated. This is accomplished by removing and not transmitting the natural silence that occurs in normal
2-way connection – the IP bandwidth is used only when someone is speaking. During the silent periods of
a telephone call additional bandwidth is available for other voice calls or data traffic since the silence
packets are not being transmitted across the network.
Configurable Dial Plan with Interdigit Timers
The SPA has three configurable interdigit timers:
• Initial timeout (T) = handset off hook, no digit pressed yet.
• Long timeout (L) = one or more digits pressed, more digits needed to reach a valid number (as
per the dial plan).
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